Harwood hit the 47-year-old with his baton and shoved him to the ground near the Royal Exchange Buildings in the City of London during the G20 protests in April 2009.

Mr Tomlinson, who was an alcoholic and slept rough for a number of years, walked around 75 yards before he collapsed and later died.

Harwood denies manslaughter on the grounds that he used reasonable force.

Giving evidence on Monday, he said he thought Mr Tomlinson was deliberately obstructing the police.

“I believed he was doing it on purpose. From what I saw he looked like he wasn’t going to move and was looking at the police as though he wanted them to move him away.”

‘Heavy responsibility’

He said he pushed Mr Tomlinson, who was walking away from a police line at the time, “firmly” after the baton strike but did not mean to push him over.

Harwood told the court that before coming across Mr Tomlinson he thought the protesters were targeting him after he tried to arrest a man for scrawling graffiti on a police carrier.

“They seemed to be goading me and shouting at me, pointing their fingers at me.

In a speech to open the defence case, Patrick Gibbs QC told jurors they were the only members of the public who would ever know the full facts of what happened that day.

“You are the only 12 members of the public who have a proper understanding of what happened that night. That of course is a privileged position, but also is quite a heavy responsibility.”

Mr Gibbs said Harwood, who had been a specialist in public order since 2004, was frightened by what was happening.

“I defy anyone to have been through that and not have had his pulse racing his heart pumping, to be sweating, to be frightened.”

‘Bad decision’

He said that the baton strike was a “bad decision”, but this was not what caused Mr Tomlinson’s death from internal bleeding, which caused a heart attack.

“With the benefit of hindsight and all the footage, using the baton was a bad decision. But it certainly did not kill Mr Tomlinson. It certainly did not contribute to his death, because it did not cause him to fall over and that’s what the Crown’s theory is about the cause of death.”

Earlier, Inspector Timothy Williams told the court that Harwood was “shocked” when he saw footage of him pushing Mr Tomlinson on television.

“He watched it and he said to me that he thought he was the officer concerned.

“He had his head in his hands, he was facing towards the ground and sort of looking up to me. He was obviously shocked.”

The court heard that a message had come from senior City officers to: “Treat the lawful protesters with kid gloves but deal with those using violence with an iron fist.”